Deaf gerbils are all ears thanks to stem cells

Deaf gerbils have recovered their hearing after human stem cells were injected into their ears.

"It's a proof of concept, and it's important because for the first time we've shown stem cells can be used to repair the ear," says Marcelo Rivolta of the University of Sheffield, UK, and head of the team that treated the gerbils.

Spiral ganglion neurons in the ear convert mechanical sound vibrations into electrical signals that the brain interprets as sound.

When these neurons get damaged or die they can't be replaced. This results in a form of deafness called auditory neuropathy, which affects about a tenth of deaf people, possibly as many as 300,000 in the UK alone, says Rivolta.

Cochlear implants can correct the main form of deafness, which occurs when the cochlea loses hair cells that register sound by bending. But neurons can't be substituted except through an expensive, risky and invasive procedure to implant an electrode directly into the brain.

Now, Rivolta and his colleagues hope to develop much simpler treatments based on the so-called otic neural progenitor stem cells they made in the lab from human embryonic stem cells, the cells in embryos that can turn into all types of bodily tissues.

Restoring ganglion neurons

Rivolta's team injected about 50,000 of the otic neural progenitor cells into single ears of 18 gerbils. The animals' spiral ganglion neurons had been deliberately destroyed with a drug called ouabain, leaving them completely deaf. The stem cells were injected into the cochlea through a tiny, drilled hole.

Post mortems showed that the stem cells turned into specialised spiral ganglion neurons in the ear.

Within 10 weeks, about two-thirds of the animals had recovered some hearing. On average, the animals recovered about 46 per cent of their hearing, as measured by their ability to respond to sounds of varying volume.

"In people, this would mean going from only being able to hear a loud truck on the street to being able to hold a conversation," says Rivolta. However, he adds that considerably more work in animals is needed to refine the procedure ? it will be years before it can be tested in people.

The team also produced cells similar to the hair cells that are damaged in the majority of deaf people, but Rivolta says much more work is needed to turn these into fully functional hair cells. "If we could replace hair cells, that would enable us to treat 80 to 90 per cent of all deaf people," he says.

Journal reference: Nature, DOI: 10.1038/nature.11415

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